This tag indicates that an image from Twitter is not the original (suffixed with :orig in the URL). Using the bookmarklet on either the direct image URL link or HTML page will always upload the original image.
In addition to images tagged with this tag, any image that matches either of the following queries are also treated as twitter samples, given that they are visually identical:
- source:*twitter.com/ md5_mismatch -upscaled status:active
- source:*pbs.twimg.com/ md5_mismatch -upscaled status:active
Make sure they are fairly identical to the original image, however. Sometimes the source might be incorrect. This doesn't factor in edits such as post #2440268.